1. Field of the Invention
This invention relates to a process for wet-drawing a wire rod through a multiple slip type wet-drawing machine.
2. Description of Related Art
The multiple slip type wet-drawing process manufactures a wire filament having a desired diameter by continuously and successively drawing a wire rod through a drawing apparatus provided with plural drawing pass stages each comprised of a die and a capstan giving a drawing force to the wire rod passed through the die to reduce a diameter of the wire rod, and lies in that the die and the capstan in at least a part of the stages are immersed in a lubricating solution to provide a velocity difference between the capstan and the drawn wire rod.
As compared with a non-slip type dry-drawing process using a dry lubricant wherein a peripheral velocity of the capstan is the same as a drawing velocity of the wire rod, the multiple slip type wet-drawing process has various merits that the drawing apparatus may be simple and compact, and a wire filament having a good surface smoothness can be manufactured and the like, and is particularly and widely used in the manufacture of wire filaments such as steel filament for steel cord and the like. Since there is the velocity difference between the capstan and the drawn wire rod, however, it is apt to cause problems such as damage of the wire rod surface, wire breakage due to the change of drawing speed and tension, premature wearing of the die and the like, so that it is important to set not only a reduction of area in the die but also the difference between the peripheral velocity of the capstan and the drawing velocity of the wire rod to a certain level, respectively.
For example, Japanese Patent No. 2614950 discloses a multiple slip type wet-drawing process wherein a working ratio of the die is set within a particular range and when a slip ratio S.sub.1 is defined by S.sub.1 =(1-v.sub.1 /V.sub.1).times.100% wherein v.sub.1 is a drawing velocity of a wire rod passed through a first die and V.sub.1 is a peripheral velocity of a capstan drawing such a wire rod, S.sub.1 is not more than 30%.
And also, JP-A-9-24413 discloses a multiple slip type wet-drawing process wherein when Vc.sub.0 =Vw.sub.0 in which Vc.sub.0 is a peripheral velocity of a final capstan and Vw.sub.0 is a passing velocity of a metal filament through a final die, a slip rate ratio Sn is defined by Sn={(Vc.sub.n -Vw.sub.n)/Vc.sub.0 }.times.100% in which Vw.sub.n is a passing velocity of a metal filament through an arbitrary die and Vc.sub.n is a peripheral velocity of a capstan drawing such a filament and is 3%.about.8%.
However, there is frequently caused a case that the problems such as damage of wire rod surface, wire breakage due to the change of drawing velocity and tension, premature wearing of die and the like are not solved even by adopting the aforementioned techniques. Particularly, such a technique remarkably comes into problem in case of increasing the drawing velocity or manufacturing high-strength steel filaments.
As a method of setting a reduction of area in the die in the manufacture of the high-strength steel filaments, for example, JP-A-9-99312 discloses a drawing method wherein when a wire drawing strain .epsilon. is defined by .epsilon.=21n(d.sub.0 /d) (wherein d.sub.0 : diameter of starting wire rod, d: diameter of a rod in each stage of the drawing step, and ln: natural logarithm) in order to provide high-strength steel filaments having a good turning property, the reduction of area in the die is 10.about.20% at 1 a stage of 0.3.gtoreq..epsilon..gtoreq.0, 15.about.25% at 2 a stage of 0.3&lt;.epsilon.&lt;3.0, and 2.about.15% at 3 a stage of 3.0.gtoreq..epsilon..
In JP-A-7-305285 is disclosed a drawing method wherein when the wire drawing is carried out so as to have a wire drawing strain .epsilon. of not less than 4.0 at a final die in order to provide high-strength steel filaments having a good ductility, 1 the reduction of area in the die used in the wire drawing at .epsilon. of less than 0.75 is (22.67.epsilon.+3)%.about.29%, and 2 the reduction of area in the die used in the wire drawing at .epsilon. of 0.75.about.2.25 is 20.about.29%, and 3 the reduction of area in the die used in the wire drawing at .epsilon. of more than 2.25 is (-6.22.epsilon.+43).about.(-5.56.epsilon.+32.5)%.
Even when the above reduction of area in the die is applied to the multiple slip type wet-drawing process, however, if the setting of the velocity difference between the capstan and the drawn wire rod is inadequate, there are caused problems such as surface damage of steel filament, wire breakage, premature wearing of the die and the like, and the turning property, ductility and the like are not so improved.